While certain tissues in the human body, such as skin, are capable of self-repair (e.g., wound healing), there are many tissues that are not. For example, articular cartilage has no innate ability to repair itself, rendering any damage thereto permanent. Articular cartilage lines opposing bone surfaces in diarthrodial joints and provides a smooth, lubricated surface for articulation. Accordingly, defects in articular cartilage tend to expand and worsen over time. Damage to the articular cartilage in joints such as the knee can lead to debilitating pain.
Typical treatment choices, depending on lesion and symptom severity, are rest and other conservative treatments, minor arthroscopic surgery to clean up and smooth the surface of the damaged cartilage area, and other surgical procedures such as microfracture, drilling, and abrasion. All of these may provide symptomatic relief, but the benefit is usually only temporary, especially if the person's pre-injury activity level is maintained. For example, severe and chronic forms of knee joint cartilage damage can lead to greater deterioration of the joint cartilage and may eventually lead to a total knee joint replacement. Approximately 200,000 total knee replacement operations are performed annually. The artificial joint generally lasts only 10 to 15 years and the operation is, therefore, typically not recommended for people under the age of fifty.
An alternative treatment is implantation of cultured neo-cartilage (i.e., immature hyaline cartilage) which can be grown in-vitro to a desired size and shape on a 3D scaffold from chondrocyte cells biopsied from the patient (autologous) or from another individual (heterologous). Examples of this process are described, for example, in U.S. Pat. Nos. 6,949,252; 7,537,780; 7,468,192; 7,217,294; and U.S. patent application Ser. No. 14/208,931. An exemplary method for 3D culture of neo-cartilage is shown in FIG. 8 and includes the steps of isolating chondrocyte cells from a biopsy, 2D growth of cells, seeding of a 3D scaffold, and two culturing steps. The first culturing step takes place under controlled pressure, oxygenation, and perfusion conditions to mimic the joint environment while the second culturing step is a 3D static culture.
Along with the neo-cartilage for implantation, multiple other surrogate tissues are simultaneously cultured in the same vessel in order to permit pre-implantation testing and verification procedures without damaging the neo-cartilage to be implanted.
Current culture containers include narrow opening flask-type containers with a sealing cap with a gas-permeable filter membrane but the 3D static culture procedure presents multiple challenges which are unmet by current culture containers. For example, the surrogates and the neo-cartilage to be implanted need to be cultured in the same conditions in a common fluid to enable validation through surrogate testing. However, in current containers, the surrogates and neo-cartilage can grow into one another as they mature and then require separation which can damage the cells and scaffolds. Another problem stems from the fact that the tissues must be submerged in fluid during the 3D static culture but the buoyancy of the cultures varies during tissue growth. The 3D static culture process takes 2 weeks and requires incubation throughout the process, taking up space in expensive incubators and limiting production efficiency and capacity using bulky flask-type containers. Additionally, the surrogates and the neo-cartilage to be implanted must be transferred from one container to another during the 2 week process and then must be removed from the container before final packaging for distribution and implantation. Manipulation of the neo-cartilage to be implanted and the surrogates through the narrow opening of the current culture containers is difficult and can cause damage to the cells. These challenges are not unique to 3D static culturing of neo-cartilage and apply to a variety of cell and tissue culturing procedures.